Looking for PCB material that can be flexed around a 17.5 cm radius

Thread Starter

cognas

Joined Feb 24, 2017
52
Folks, is there any PCB material that can be printed, then flexed. I know that "flexible PCBs" are shown all over the web, but they resemble ribbons more than what I have in mind. I'd like something pretty stiff, to prevent flutter when it is moving at speed through air. I want to make a propeller globe - a "persistence of vision" globe that spins a semi-circle of LEDs to give the illusion of a spherical globe (see YouTube "POV globe"). I want to use really tiny LEDs - https://www.adafruit.com/product/3341 - and as they would be challenging to solder to, I want to surface-mount them. The "sphere" would be 35cm diameter, so the boards would have to be bendable around a 17.5 cm radius.
Is there anything available that could be manufactured in a home-workshop?
 

jpanhalt

Joined Jan 18, 2008
7,893
Years ago, I got some full panels of copper (1 or 0.5 oz?) on very thin FR4. It is quite flexible and might meet your spec. for 35cm diameter. I use it for shielding. Maybe you should consider whatever is used (pre-peg?) for the intermediate layers on multilayer PCB's?
 

dl324

Joined Mar 30, 2015
8,906

Thread Starter

cognas

Joined Feb 24, 2017
52
Thanks very much for those, Folks. I'll look into them further tomorrow (it's late now).
 

ronsimpson

Joined Oct 7, 2019
115
upload_2019-10-14_17-23-14.png
In one of the videos there is a aluminum circle that spins. It could have a flex PCB glued to it.
upload_2019-10-14_17-25-6.png
 

TeeKay6

Joined Apr 20, 2019
382
Thanks very much for those, Folks. I'll look into them further tomorrow (it's late now).
@cognas
Any commercial PCB fabricator can answer your question. Rather than a flexible PCB, perhaps you could consider a crescent shaped rigid PCB with LEDs emitting from the edge?
 

Mark Hughes

Joined Jun 14, 2016
395
@TeeKay6 has a good idea. Just make a flat, semi-circular rigid pcb from OshPark or similar. If you order from a PCBFab, you're going to have to buy an entire panel at a minimum, and that's going to cost some coinage. Your second best bet is to call a PCB fabhouse and ask their engineering department. They'll have a variety of materials on hand.

You can try AdvancedAssembly (aapcb.com), SierraCircuits (protoexpress.com), etc.... The hard part is going to be getting somebody to talk to you without a fab-drawing in hand.

Do you at least have a schematic? You might try pcblayout.com -- they might be able to help you.

Here's another thought. What about one of those rgb-led strips? https://www.ebay.com/itm/5M-RGB-5050-Waterproof-LED-Strip-light-SMD-44-Key-Remote-12V-US-Power-Full-Kit/302383732527

What are you going to use for a commutator when you spin it?
 

Thread Starter

cognas

Joined Feb 24, 2017
52
@cognas
perhaps you could consider a crescent shaped rigid PCB with LEDs emitting from the edge?
Yes, I had thought of that, but the LEDs I was thinking of using (DotStar 2020) shine directly away from the substrate (PCB in this case), so doing it that way would involve some sort of arrangement to mount them at 90 degrees to the board. Also, a print that size would be on a 35 x 17.5 cm board (minimum), which would be a large print, and I think they charge by area. And a third (possibly ridiculous) reason is that it would reduce wind resistance to put it edge-on to the motion.
I had thought of using copper foil and sticking it to a substrate myself - but getting it stuck well enough to etch and solder to is, I fear, outside of my abilities. Therein lie dragons!

My idea hasn't gone beyond ambition yet - I haven't bought any materials or experimented with anything physical yet

Thanks for the pictures, by the way - though I had seen all of them apart from the "Globe of death" - but that's OK, I'm not going to make one of those.
 

Thread Starter

cognas

Joined Feb 24, 2017
52
@TeeKay6 has a good idea.
Coinage.
What about one of those rgb-led strips?
commutator?
"Coinage" - yes, I'm ever-conscious of that - though this project is going to cost a bit anyway. A lot of the ambition is to make a better one than any I see on YouTube, by making a higher resolution picture, using smaller dots. This means (a) higher frequency to get 550, 2mm dots around the equator, and (b) smaller LEDs. The DotStar RGB LEDs that seem quite attractive are 2mm x 2mm, which is pretty tiny - though I can't use a single row of them - the frequency required would be too high. Packing them at 4 per cm gives me 220 LEDs on the semi-circle. However, surface-mounting them without specialist equipment, or alternatively soldering 6 wires to each of them may turn out to be a bridge too far, so I had also considered another possibility - using 2mm LEDs, but individual R, G and B, on each of three semi-circles at 120 degrees spacing as seen from the North (or South) pole (660 LEDs alltogether). I'm currently constructing an experiment to see if POV colour-adding will work OK (making a dot of R, then G then B in the same place should give me a white dot). A problemette in using individual LEDs would be that they would require resistors.

I looked at your link to the strips of RGB lights, but the smallest you can get in a strip is 5050 - 5MM square, and it's the 2mm units that attract me. There are several hurdles to overcome, however -
1) they don't come on a strip. Maybe the manufacturer will get around to that, but I haven't seen it advertised anywhere.
2) the advert for the individual units mentions the difficulty of soldering to them. My soldering is fine - but 6 wires onto a 2mm square for 220 LEDs is more than I have ever done previously. I'd give it a go, but it would be an adventure.
3) I can't spin them at 1800 RPM (30 RPS) with a refresh rate of 550 per rev, and feed serial data of 32 bits each along a 220 unit string. The frequency required is more than the chip in them can handle. I could still do it, but by breaking them into 5 zones - which would be sensible anyway. A 2mm dot at the equator takes a much higher frequency than a 2mm dot at 80 degrees latitude. I wonder if the banding would be obvious !

"Commutator" - I had a couple of ideas - I could have a generator made from a coil on the rotating part, with a few magnets on the stationary part - but with so many LEDs, the current could be quite high, so the generator would have to be capable of several amps. I haven't worked it out, but I think up to 8A. On the balance, a simple DC slip-ring with brushes, smoothed with a capacitor is probably the simpler solution.

Thanks for the manufacturer links. I don't have a schematic yet, though it will be a simple one when I decide how to make the thing.

Refresh rate is too high for most low-cost processors, but I can display the picture from memory, and for slow-moving movies (eg continental drift, position of the ISS, day/night, etc), I can refresh the memory at my leisure.

A forthcoming problem (I'll cross that bridge when I get there) will be to calculate he position of the day/night terminator. It is at 23.5 degrees to the axis at the solstices, and moves to 0 degrees at the equinoxes. Spherical geometry will be another adventure - though https://24timezones.com/#/map has clearly sorted it out.
 
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